Electric circuit interrupter



March 8, 1938. z 2,110,690

. ELECTRIC CIRCUIT INTERRUPTER Filed Feb. 20. 1936 Fig 1.

Inventor: Georg Z i erahn,

b am

is ttorneg,

Patented Mar. 8, 1938 ELECTRIC CIRCUIT INTERRUPTER (leer-g Zierahn, Berlin, Germany,

asslgnor to General Electric Company, a corporation of New York Application February 20, 1936, Serial No. 64,959 In Germany March 15, 1935 6 Claims.

My invention relates to electric circuit interrupters and more particularly to an interrupter adapted to be used with devices having a positive temperature-resistance coefiicient, such as tungsten lamps.

According to my invention, the interrupter comprises a resistance element having a negative temperature-resistance coefiicicnt and being electrically connected in series with the operating device, such as the filament of an incandescent lamp, and a thermal switch which is electrically connected in multiple with the said resistance element and is heated by it. One of the advantages of such a resistance element is that when the circuit is closed a small current flows through the filament oi the lamp and heats it so that it glows but slightly or not at all. Then when the said resistance element becomes heated and closes the thermal switch the full line voltage is impressed across the filament so that it glows. brightly. Thus the usual surge oi current which {occurs when the circuit is closed is prevented from passing through the filament by the resistance element. This is of great importance for example in the case of large incandescent lamps and particularly when several devices are con nected in series which have difierent values of power consumption and heating time.

Further features and advantages of my invention will appear from the following detailed description of species thereof.

In the drawing, Fig. 1 is an elevation of an interrupter comprising my invention connected to an incandescent lamp, and'Fig. 2 is an elevation of an incandescent lamp having an interrupter oi modified form mounted in the bulb of the lamp.

Referring to Fig. 1, the interrupter l0 comprises a bulb I I which may be similar to an incandescent lamp bulb. A resistance element I2 is mounted in said bulb II on a pair of conductors i3, I4. The said resistance element 12 preferably consists of an oxide which is conductive at ordinary room temperatures and has a high negative temperature-resistance coeflicient, such as a body of uranium dioxide. A thermal switch l5, which may consist of a bimetallic strip, is also con nected across the conductors l3, H in multiple with the resistance element I2 and is disposed adjacent to said resistance element so as to be heated thereby. The said resistance element I2 is connected in series with the filament iii of an incandescent lamp H by a conductor Hi. The

said filament i6 is preferably of tungsten, which has a positive temperature-resistance coefiicient.

The lamp and interrupter are connected to the line at H and 20.

The operation of the device is as follows:

When the circuit is closed, a small current first flows through the resistance element l2 and 5 filament l6 which heats the filament at most to a dark red glow. When the resistance element I2 becomes warm as a result of the current flowing therethrough, it heats the switch it and causes it to close. The filament i6 is then connected 10 across the full line voltage and it glows brightly. The resistance element l2 and switch ll then cool down until the said switch is opened to again connect the said resistance element in series with filament I6 which glows but slightly as a result of the reduced current.

In the device shown in Fig. 2, the interrupter and filament are mounted in the same bulb 2|. The thermal switch 22 in this case consists of a mercury switch mounted within a tubular resistance element 23 of the same type as the resistance element I2 in Fig. 1. The switch 22 is protected from the radiation of the filament I by a disc 24 which may be of mica. The electrical connections and operation of this device are the same as that shown in Fig. 1.

The use of a resistance element of semi-conducting material such as uranium dioxide has the advantage that it may be made quite small. Moreover, its resistance drops to such an extent during the heating that no great surge of current occurs at the consuming device, or filament, when the resistance element is short-circuited.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit interrupter comprising a bulb containing a resistance having a negative temperature-resistance coefiicient and a thermal switch electrically connected in multiple with said resistance and disposed adjacent to'said resistance 40 V so as to be heated thereby.

ance element having a negative temperatureresistance'coefllcient and a thermal switch electrically connected in multiple with said resistance element and disposed adjacent to said resistance element so as to be heated thereby, and a filament having a. positive temperature-resistance coemcient and electrically connected in series with said resistance element.

6. In a device of the type described, the combination of a bulb, a resistance element in said bulb having a negative temperature-resistance coemcient, a thermal switch in said bulb electrically connected in multiple with said resistance element and disposed adjacent to said resistance element so as to be heated thereby and a filament in said bulb having a positive temperature-resistance coeflicient and electrically connected in series with said resistance element, said switch being spaced away from said filament so as to be unaflected in its operation by the heat radiation therefrom.

GEORG ZIERAHN. 

